USB-Audio: Add Use Case for Arturia Minifuse 2

USB-Audio: Add Use Case for Arturia Minifuse 2

Arturia Minifuse 2
(https://www.arturia.com/products/audio/minifuse/minifuse2)
is an USB audio interface with 2 mono inputs and 2 channel outputs.
It uses 1 subinterface with 4 capture and 4 playback channels:
Capture channels:
- Mic/Line/Inst 1 (Mono)
- Mic/Line/Inst 2 (Mono)
- Loopback (Stereo, L+R)

Playback:
- Main (Stereo, L+R)
- Loopback (L+R)

The Loopback capture and playback are intended to ease recording sound
from the computer, e.g if you're doing a podcast and want to record
something that plays from the computer. Of course us linux user don't
need that, since we have many tools able to do that.

However, without a dedicated use case, alsa treats the channels as
surround 4.0, which make the card difficult to use.

At this stage, no controls are available.

TODO/FIXMEs:
- add a channel map override on the pcm device ?

Fixes: https://github.com/alsa-project/alsa-ucm-conf/pull/145
Signed-off-by: Clément Hermann <nodens@debian.org>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>